This invention relates to improved chemical processing units and the processes which use these units. More particularly, this invention relates to a solid fuel gasifying unit and a gas fractionating unit which may be operated in sequence and/or with other chemical processing units, and which use a gravitational driving force to circulate solid material in a smooth and continuous fashion.
The threshold or common denominator of all commercial chemical reaction systems is that they must be economical to operate. In the prior art, solid fuel gasifying units have been cost-justified when designed to handle relatively high feed rates; that is, feed rates in excess of 500 tons per day. However, owners of small coal deposits or of other sources of solid fuel materials, such as lumber mills, often cannot justify the expense of constructing a solid fuel gasifying system due to the relatively small feed rates at which they would operate.
The construction of gasifying units handling relatively low feed rates has heretofore been unsatisfactory because the design of a unit to operate around a pressure of 200 psig, as is common in the industry, has required small diameter piping which made physical installation and inspection of the interior of the unit difficult, if not impossible. Thus, solid fuel owners who would otherwise wish to generate steam and other useful, gaseous products from coal or other solid fuel feedstocks have been unable to do so. Accordingly, it has been desirable to furnish at least a partial solution to this problem by providing an efficient gasifying process and unit which operates at a relatively low pressure, thereby allowing higher gas volume rates and piping of correspondingly larger diameter.
Another major problem faced by prior operators of solid particle circulating units, including solid fuel gasifying units and gas fractionating units, is the frequent instance of valve malfunction due to solids accumulation and abrasion. In solid fuel gasifying units which employ solid catalytic reagents, the valves which surround the lock-bin screw conveyor in the feed line and which regulate the flow of reagent through the system are particularly prone to failure. In gas fractionating units, the valves which direct the flow of the circulating reagent powder in the fractionating zones are particularly troublesome. Solids accumulation in or near these valves can make them difficult to open, close, and control, and can significantly affect the performance of the unit. If sufficiently serious, valve malfunction may force a costly unit shutdown for repair or replacement.
The problems suggested in the preceding are not intended to be exhaustive, but rather are among many which tend to reduce the effectiveness of prior solid fuel gasifying systems and gas fractionating systems. Other noteworthy problems may also exist, however, those presented above should be sufficient to demonstrate that such units appearing in the prior art have not been altogether satisfactory.